Pebble heater



June 12, 1956 Filed Jan. 3, 1952 FIG.

D. J. QUIGG PEBBLE HEATER 5 Sheets-Sheet l INVENTOR.

D. J. QUIGG warml ATTORNEYS June 12, 1956 J, QUIGG 2,750,181

PEBBLE HEATER Filed Jan. 3, 1952 5 Sheets-Sheet 2 A T TORNEKS' D. J.QUIGG PEBBLE HEATER June 12, 1956 5 Sheets-Sheet 3 Filed Jan. 5, 1952FIG. 3.

INVENTOR.

D. J. QUIGG BY 4 T TORNEYS United States Patent PEBBLE HEATER Donald J.Quigg, Bartlesville, Okla., assignor to Phillips Petroleum Company, acorporation of Delaware Application January 3, 1952, Serial No. 264,80926 Claims. (Cl. 263-19) This invention relates to pebble heaters. In oneof its morespecific aspects, it relates to improved pebble heaterapparatus. in another of its more specific aspects, it relates tonsingle shell pebble heater apparatus, In another of its morespecificaspects, it relates to pebble heater apparatus having only a singleupright chamber containing a contiguous gravitatingv mass therein. Inanother of its more specific aspects, it relates to the conversion ofhydrocarbons in pebble heater apparatus.

Apparatus of the so-called Pebble Heater type has been utilized inrecent years for the purpose of heating fluids to elevated temperatures.Such apparatus is especially suited for use in temperature ranges abovethose at which the. best available high temperature structural alloysfail. Thus, such. equipment may be used for superheating steam or othergases and for the pyrolysis of hydrocarbons to produce variable productssuch as ethylene and acetylene, as well as for other reactions andpurposes. Conventional pebble heater type apparatus includes tworefractory lined contacting chambers disposed one above the other andconnected by a refractory lined passageway or pebble throat ofrelatively narrow cross-section.

Refractory. solids of flowable size and form, called pebbles, are passedcontinuously and contiguously through the system, flowing by gravitythrough the uppermost chamber, the throat, and the lowermost chamber,and are then conveyed to the top of the uppermost chamber to completethe cycle.

Solid heat exchange material which is conventionally used in pebbleheater apparatus is generally called pebbles. The term pebbles as usedherein denotes any solid refractory material of flowable size and form,having strength, which is suitable to carry large amounts of heatfromthepebble heating chamber to the gas heating chamber without rapiddeterioration or substantial breaking. Pebbles conventionally used inpebble heater apparatus are ordinarily substantially spherical in shapeand range from about /s inch to about 1 inch in diameter. In a hightemperature process, pebbles having a diameter of between A to /s inchare preferred. The pebbles must be formed of a refractory material whichwill withstand temperatures at least as high as the highest temperatureattained in the pebble heating chamber. The pebbles must also becapable. of withstanding temperature changes within the apparatus.Refractory materials, such as metal alloys, ceramics, or othersatisfactory material may be utilized to form such pebbles. Siliconcarbide, alumina, pericla se, beryllia, Stellite, zirconia, and mullitemay be satisfactorily used to form such pebbles or may be used in.admixture with each other or with other materials. Pebbles formed ofsuch materials, when properly fired, serve. very well in hightemperatures, some withstanding temperatures up to about 4000 F. Pebbleswhich are used may be either inert or catalytic as used in any selectedprocess.

The pebbles are heated in one of the chambers. (preferably the upperone) by direct contact therein with hot gases, usually combustionproducts, to temperatures genorally in the range of 1400 F. to 3200" F.The hot pebbles are thereafter contacted with the fluid to besuperheated or reacted, as the case may be, in the other chamber.Generally, pebble inlet temperatures in the second chamber are about F.to 200 F. below the highest temperature of the pebbles within the firstchamber. In processes for the production of ethylene from light hydro,-carbons, such as ethane, propane, or butane, the. pebble temperatureinthe reaction chamber is usually in the range of 1200 F. to 1800" F.For the production of acetylene by pyrolysis of hydrocarbons,temperature in the range of 1600 F. to 3000 F. are desirable.

In the past, considerable trouble has been encountered in the operationof pebble heater apparatus for the. reason that pebbles which are heatedin the pebble heating chamber are not all heated to a uniformtemperature. For this reason the pebbles which are introduced into theupper end portion of the reaction chamber lack the desired uni formityof temperature which would give the best reaction of feed within thatreaction chamber. The result has been that a portion of the feed stockhas been overcracked and-a portion of the feed stock has beenunder-cracked by reason of the contact with pebbles heated totemperatures above. and below that desired for reaction of the feed.This difliculty in obtaining uniform temperatures of pebbles within thepebble heating chamber is due principally to the fact that the pebbleheating chamber is one of large cross-section, and the gas flow patternswithin such a chamber containing a contiguous gravitating pebble massarev such as to permit a considerably greater contact time between gasand pebbles in one section of the chamber than is obtained in anothersection of the same chamber.

Another disadvantage of the conventional pebble heater type apparatus isthat it is quite expensive to construct, partly because of the fact thatthe two chambers should be supported one above the other so as to obtaingravitating flow of pebbles throughout the entire length of the system.Such a structure requires a considerably greater supporting structurethan is necessary for one of lesser strength. Another disadvantage inconstruction of the conventional pebble heater type apparatus is that along elevator system is necessary, thus, posing many operationalproblems.

By at least one aspect of this invention, at least one of the followingobjects of the invention is attained.

An object of this invention is to provide improved pebble heaterapparatus. Another object of the invention is to provide a singlechamber pebble heater apparatus. Another object of the invention is toprovide an improved method for reacting hydrocarbons in pebble heaterapparatus. Another object of the invention is to provide an improvedmethod for heating pebbles in pebble heater apparatus. Other and furtherobjects and advantages will be apparent to those skilled in the art uponstudy of the accompanying discussion and the drawings.

Broadly speaking, this invention comprises a single chamber pebbleheater apparatus, a single chamber forming a single Zone for reaction ortreatment of gaseous materials within that chamber. The entire amount ofpebble heating is obtained in the pebble recycle system utilized. forelevating the pebbles which are removed from the bottom of the reactionchamber, to the upper end portion of the chamber. A gas lift type ofrecycle system is utilized for returning the pebbles to the upper endportion of the reactor chamber. The lift-gas is heated to a hightemperature prior to its contact with the pebbles. When certain gasesare utilized as the lift-gas it is necessary to introduce largerquantities of that gas into the gas lift than when utilizing other gasesin order to maintain entrainment of the pebbles throughout the entire lngth of the gas lift.

When the heating or lift-gas is at a high temperature and when that gashas a. high heat transfer coeflicient,

the pebbles are subjected to considerable mechanical and thermal shockif the total amount of lift-gas is introduced into the bottom end of thegas lift. I have devised a method whereby the pebbles can be entrainedin the lower end portion of the gas lift and maintained in entrainmentthrough that lift without substantial mechanical or thermal shock. Thisresult is obtained by introducing only a portion of the lift-gas intothe lower end of the gas lift. That portion of the gas is sufiicient toinitially entrain and fiuidize the pebbles in the lower end of the gaslift. The quantity of pebbles is sufiiciently large with respect to thequantity of heating gas that thermal shock is substantially obviated.-As pointed out above, however, the heat transfer between the hot gasand the pebbles causes a reduction in volume of the gas. For

this reason, the pebbles tend to form a denser phase as they proceedupwardly through the gas lift. In order to offset this reduction involume of the gas and in order 'to make available a sufiiciently largenumber of B. t. u.s

to heat the pebbles to the high temperatures required in the system, Iintroduce additional heating gas portions obviates thermal shock of thepebbles.

Heating the pebbles in this manner, results in delivering each of thepebbles to the upper end of the reactor at a temperature which issubstantially the same as that of any other pebble, thereby obviatingthe difficulty of non-uniform pebble heating encountered when using theconventional multi-chamber pebble heater system. It

should also be noted that the height of the pebble heater system of thisinvention is only about one-half the length of pebble heater systemswherein two chambers are disposed one above the other.

Better understanding of this invention will be obtained upon referenceto the drawings. Figure 1 is a schematic 'fiow diagram of the pebbleheater system and feed and effluent lines connected with such a system.Figure 2 is a schematic representation of a portion of the feed andeffluent lines connected to the gas lift together with a startup systemprovided in connection with the gas lift. Figure 3 is a schematicrepresentation of a portion of the feed and effluent lines connected tothe gas lift together with a preferred modification of the startupsystem of this invention.

Referring particularly to the device shown in Figure 1 of the drawings,pebble heater apparatus 11 comprises an upright elongated shell 12,closed at its upper and lower ends by closure members 13 and 14,respectively. Pebble inlet conduit 15 extends into the upper end portionof shell 12, preferably being centrally disposed in closure member 13.It is within the scope of this invention, however, to utilize aplurality of pebble inlet conduits uniformly disposed over the top ofthe pebble heater apparatus. When a plurality of inlets is utilized, itis desirable to provide a pebble surge chamber in pebble inlet conduit15 so as to obtain uniform pebble flow to all portions of the top of thepebble bed within chamber 11. Gaseous effiuent conduit 16 is provided inthe upper end of shell 12, preferably in closure member 13. Pebble-outlet conduit 17 extends downwardly from the bottom extends upwardlyinto the central portion of gas-pebble 'separator chamber 19. Pebbleinlet conduit 15 is connected at its upper end to the lower end portionof separator 19.

Gaseous inlet conduit 21, having flow control valve 22 providedintermediate its ends, is connected to thelower end portion of pebbleinlet conduit 15. Gaseous material inlet header 23 is provided so as toat least partially encircle pebble inlet conduit 15 intermediate itsends and communicates with the interior of the pebble inlet conduit.Gaseous material outlet material conduit 24 is connected to the upperend portion of pebble inlet conduit 15 at a point downstream ofseparator chamber 19. Separator chamber 25 is connected intermediate itsends to the upper end portion of separator chamber 19 by means ofconduit 26. Indirect heat exchanger 27 is connected to the upper endportion of separator 25 by means of conduit 28, that conduit beingprovided with flow control valve 29 intermediate its ends. Conduit 31extends from indirect heat exchanger 27 and is connected to vent conduit32, the latter conduit having flow control valve 33 providedintermediate its ends. Outlet conduit 31 is also connected to conduit 34which is in turn connected to a pressurizer, such as blower 35. Conduit34 is provided with flow control valve 36 intermediate its ends and aninlet conduit 37, provided with flow control valve 38, is connected toconduit 34 intermediate flow control valve 36 and blower 35. Conduit 24is directly connected to conduit 28 by means of by-pass conduit 39, thelatter conduit being provided with a flow control valve 41 intermediateits ends. A second by-pass conduit 42, being provided with a flowcontrol valve 43, connects conduit 24 directly with conduit 34 at apoint upstream of flow control valve 36. Feed conduit 44 extends throughindirect heat exchanger 27 and through an auxiliary indirect heatexchanger 45 and is connected to the lower end of shell 12 andcommunicates with the chamber within that shell, preferably throughbottom closure member 14.

'outlet conduit 51 extends from the portion of the combustion chamberconnected to the air and fuel inlet conduits. Conduit 51 is divided intotwo portions, one portion 52 extending to the lower end of elevator 18.Flow control valve 53 is provided intermediate the ends of conduit 52. Asecond portion of combustion gas outlet 51 designated as conduit 54extends to inlet header 23. Conduit 54 is provided intermediate its endswith a flow control valve 55. Conduit 56 extends from conduit 52 toindirect heat exchanger 45 and is provided with flow control valve 57intermediate its ends. Gaseous effluent conduit 58 extends from indirectheat exchanger 45.

Conduit 59 extends from blower 35 to the upstream end of the section offurnace 46 which is not connected with the fuel and inlet conduits. Flowcontrol valve 61 is provided intermediate the ends of conduit 59.Conduit 62 extends from the downstream end of the section of furnace 46which is connected to conduit 59 and is connected at its downstream endto conduit 52 downstream of flow control valve 53. Conduit 63 extendsfrom a juncture with conduit 52, intermediate the juncture of conduits52 and 62 and elevator 18, and is connected at its upper end to theupper end portion of elevator 18. Flow control valve 64 is provided inthe upper end portion of conduit 63. A plurality of connecting conduits65, 66, 67 and 68 extend between conduit 63 and spaced points along thelength of elevator 18. Flow control valves 69, 71, 72 and 73 areprovided in connecting conduits 65, 66, 67 and 68, respectively. It isusually sufficient to utilize one connecting conduit for the addition ofhot gaseous material about every ten feet along the length of theelevator. If desired, more or less of these connecting conduits anddifferent spacings may be utilized. .A,pebble flow. controller 74 isprovided intermediate the ends of pebble outlet conduit 17. This flowcontroller may be any one ofthe conventional controllers, such as a starvalve, a gate valve, a rotatable feeder, a vibratory feeder, or thelike.

Referring particularly to Figure 2 of the drawings, like numeralsidentify parts described in connection with Figure 1 of the drawings. Inthe device shown in Figure 2, a plurality of pressure drop detecting;devices such as manometers 75, 76, 77, 78, 79 and 81 are spaced apartalong the lower portion of elevator 18. Although. the manometers. havebeen shown schematically as liquid type, it should be, noted that theconventional dry type manometer is preferred because of the hightemperatures encountered in the gas lift. Liquid type manometers aresuitable when spaced from the gas pebble conduit sufficiently tomaintain the liquid in a cooled condition. It is preferred that thesepressure drop sensing devices be spaced apart a distance of betweenabout one and two feet through at least the lower one-third of theelevator. The manometers are operatively connected tocontrollers 82, 83,84, 85, 86 and 87, respectively. Auxiliary gas conduits 88, 89, 91, 9293 and 94 extend between conduit 63 and elevator 18. These conduits arespaced so that one of these conduits is connected to elevator 18 at apoint closely approximating the lower end of each of the pressure dropsensing devices. Valves 95, 96, 97, 98, 99 and 101 are provided forcontrol of flow in conduits 88, 89, 91, 92, 93 and 94, respectively, andare operatively connected to controllers 82, 83, 84, 85, 86 and 87,respectively. In the construction shown in the modification of Figure 2,valves, 69, 71, 72, 73 and 64 are connected to a power source, notshown. Valve 102 is provided in the connecting conduit intermediate thepower source and the lowermost valve 69. Controllers 82, 83, 84, 85, 86and 87 are also connected to a power source, not shown. Valve 103 isprovided in the control line between the power source and the lowermostcontroller 82.

Referring particularly to Figure 3 of the drawing, the same-numeralsidentify parts described in connection with Figure 1 and Figure 2 of thedrawings. In the device shown in Figure 3, a plurality of temperaturesensing members, such as thermocouples, are provided in the shell ofelevator 18 at spaced points along at least the lower one-third of thelength thereof. Thermocouples 10,7, 108, 109, 111, 112, 113 and 114 areschematically shown in Figure 3 of the drawings. Thermocouple 107 isprovided above connecting conduit 67 which has valve 72 providedtherein. Thermocouple 108 is provided intermediate conduits 94 and 67,thermocouple 109 is provided intermediate conduits 93 and 94,thermocouple 111 is provided intermediate conduits 92 and 93,thermocouple 112 is provided intermediate conduits 91 and 92,thermocouple 113 is provided intermediate conduits 89 and 9.1 andthermocouple 114 is provided intermediate conduits 88 and 89.Thermocouples 107 and 108 are operatively connected to differentialcontroller 115, which is. in turn operatively connected to valve 101.Thermocouples 108 and 109 are operatively connected to differentialcontroller 116 which is in turn operatively connected to valve 99.Thermocouples 109 and 111 are operatively connected to differentialcontroller 117, which is in turn operatively connected to valve 98.Thermocouples 111 and 112 are operatively connected to differentialcontroller 118 which is in turn operatively connected to valve 97.Thermocouples 112 and 113 are operatively connected. to differentialcontroller 119 which is in turn operatively connected to valve 96.Thermocouples 113 and 114 are operatively connected to diiferentialcontroller 121 which is in turn operatively connected to valve 95. Inthe construction shown in the modification of Figure 3, valves 69, 71,73 and 64 are connected to a control source, not shown, as discussed inconnection with Figure 2. Valve 102 is provided in the connectingconduit intermediate the control source and the lowermost valve 69.Valve 72 is also connected to a control source, not shown, by a separateconduit and valve 122 is provided in the connectingcorp duitintermediate the control source and valve 72, Differential controllers115, 116, 117, 118, 119 and 121 are also connected to a. power source,not shown. Valve 123' is provided in the control line between the powersource and the lowermost difi'erential controller 121.

In the operation of the pebble heater of this invention, pebbles areintroduced into the upper end portion of chamber 11 through pebbleinletconduit 15 and form a contiguous, gravitating, gas-pervious masswithin that zone. This mass of pebbles continues as a contiguous beddownwardly through the entire length of the chamher and through pebbleoutlet conduit 1.7 to pebble flow controller 74. The pebbles are fed bymeans of pebble feeder 74 into the lower end portion of gas liftelevator 18. A lift-gas is introduced into, the lower end portion ofelevator 18 at a temperature of at least about 2000 F. and at asufiicient volume and velocity to initially entrain the pebbles, in thelower portion of the elevator. Additional portions of the hot gas areintroduced into the elevator at spaced points along its length throughconduits 65, 66, 67, 6 8 and 63. Whenthe pebble entraining gas streamenters gas-pebble separator chamber 19, the velocity of the pebbles isso reduced as to follow those pebbles to settle from the gas streamwithin. separator 19.

In one aspect of the invention, fuel and air are introduced into furnace46 through conduits 48 and 49. The fuel and: air are burned and theresulting hot combustion products are passed by means of conduits, 51and 52 to the lowerend of elevator 18. As pointed out above, additionalportions of the hot gas stream are introduced at spaced points alongthelength of the elevator. The efiluent. gas is removed from the upper endportion of chamber- 19 through conduit 26. This effluent gas carrieswith it the pebble fines from the system and is passed through separatorchamber 25, which is a cyclone type separator. The pebble fines areseparated from the efiluent gas and are removed from the bottom portionof that chamber. The effluent gas is removed from the upper end portionof separator chamber 25 and is passed through indirect heat exchanger 27and is removed from the system through outlet conduit 31 and ventconduit 32.

The feed tothe pebble heater system, whether it be a hydrocarbon feed ora gaseous material to be treated, is passed by conduit 44 throughindirect heat exchanger 27 in indirect heat exchange with the gaseouseffluent from the gas lift. A second portion of the combustion gasesobtained from furnace 46, is passed by means of conduit-s 51, 52 and 56into. indirect heat exchanger 45 and is vented through conduit 58. Thefeed which is preheated in the indirect heat exchange in exchanger 27 ispassed through indirect heat exchanger 45 and is additionally preheatedby means of the second portion of combustion gas from: furnace 46 in theindirect heat exchange within exchanger 45. Thepreheated feed isthenintroduced into the lower portion of chamber 12;.

In elevating the pebbles to the upper end portion of the elevator, it isnecessary to maintain. at least a minimum pebble velocity of 5 feet persecond within the elevator. In order to maintain this minimum velocity,it is necessary to introduce a sufficieut amount of gas into the gaslift to intially entrain the pebbles and to maintain the entrainmentthroughout the length of the elevator. When entraining gas is,introduced only into the bottom portion of the elevator, it is necessarytomove the pebbles at a velocity in the neighborhood of between about 25and feet per second in the lower portion of the elevator in order toobtain the desired pebble velocity at the top of a 50-foot lift. Thespecific initial pebble velocity which is required in such an operationis dependent upon the particular lift-gas utilized. By operating in themannor of this invention, it is possible to reduce the initial pebblevelocityto within the range of 10 feet per second to 25' feet persecond, depending upon the specific lift-gas utilized. The initialpebble velocity will be dependent cracked during the heating and liftingsteps.

-volume of the heating gas. {heating gas, combustion products fromfurnace 46 may be vented through conduit 104 and valve 105, valve 106jupon the distance between the auxiliary gas inlets in the gas lift.

Combustion products resulting from the burning of a .hydrocarbon feedand air are satisfactorily utilized as in the gas lift by burning freeoxygen and hydrogen in the furnace and utilizing the resulting steamproduct as the lift-gas. When steam is utilized as the lift-gas, it isnecessary to utilize a higher initial pebblevelocity than is used whenproducts of hydrocarbon combustion are used as the lift-gas. This highervelocity is required because of the greater amount of shrinkage in thevolume of gas due to the higher rate of heat transfer obtained withsteam than with hydrocarbon combustion products.

In another aspect of this invention, a gaseous material such as methaneor hydrogen is introduced into conduit 34 through flow control valve 38and conduit 37. This gaseous feed is pressurized in blower 35 and ispassed by means of conduit 59 into the portion of furnace 46 which isnot connected with inlet conduits 48 and 49. The gaseous feed is heatedto a high temperature, preferably at least 2400 F. by means of theindirect heat exchange with the combustion products and by radiant heatwithin furnace 46. The preheated gaseous material is then passed intothe lower portion of gas lift 18 by means of conduit 62 and into spacedpoints along the length of elevator 18 through the various supplementalinlet conduits. The advantage which is obtained by use of these gases asa lift-gas material is that the pebbles can be heated to a somewhathigher temperature than when products of hydrocarbon combustion areused. A feed of hydrogen provides a substantially higher temperature forthe pebbles than does the preheated methane. When methane is used as thelift-gas, a portion of that gas is After the methane and its productsare removed from the upper end of separator chamber 19 and are passedthrough indirect heat exchanger 27 they may be vented to the atmosphere,but are preferably utilized as a preheated feed for furnace 46. Whenhydrogen is used as the lift-gas, the hydrogen is removed from the upperend portion of separator chamber 19, passed through separator 25 andindirect heat exchanger 27. When utilizing this type of lift-gas, it isordinarily not necessary to utilize the auxiliary heat exchanger 45 forpreheating the feed. However, the auxiliary heat exchanger 45 may beutilized so as to obtain a desired feed temperature. The hydrogenremoved from indirect heat exchanger 27 is passed by means of conduits31 and 34 into blower 35 wherein it is pressurized and once againrecycled through the indirect heat exchange in furnace 46 and into gaslift 18.

As pointed out above, one of the important features of this invention isthat each of the pebbles is raised to a temperature which issubstantially the same as the temperature of each of the other pebbles.In one additional heating step, a portion of the heating gas may bepassed into pebble inlet conduit 15 through inlet header 23 and causedto flow upwardly through the gravitating mass of pebbles within thatconduit. The gaseous effiuent is removed from that conduit throughoutlet conduit 24. Pebble inlet conduit 15 is considerably smaller incrosssection than any of the conventional pebble heater chambers and forthis reason the heating which is obtained within conduit 15 issubstantially the same for all pebbles. An increase of 200 F. to 300 F.in pebble temperature ican be obtained in this short section of a pebbleinlet conduit by direct heat exchange with a relatively small Ifhydrogen is used as the being closed. Hydrogen can then be passed bymeans 10f conduits 62, 52 and 54 into the pebble inlet conduit.

as the lift-gas, the portion of hydrogen from conduit 24 is recycledthrough conduit 34 to blower 35.

The modification shown in Figure 2 of the drawings is particularlyimportant in the operation of a pebble heater in which close control ofpebble How is maintained in the gas lift elevator. A pebble velocity ofat least 5 feet per second is necessary to prevent the pebbles fromfalling out and collecting as a dense mass in the lower end portion ofthe pebble elevator. In order to obtain startup of the pebble heaterdevice after pebble drop out in the elevator has occurred, it has beennecessary to withdraw the mass of pebbles from the elevator so as toobtain fluidization of those pebbles a few at a time. Ordinarily, themass of pebbles will not reach a height much greater than aboutone-third the length of the elevator. For that reason, this startupmodification is preferably provided only in the lower one-third of thegas lift. If longer gas lifts are utilized so that greater masses ofpebbles are present in the lift, more of the control elements may beused so as to extend to the top of the pebbles when they are formed as acompact bed after dropping out of the gas stream.

In the operation of this device for startup of the pebble heaterapparatus, valve 102 is manipulated so as to allow a source of power toclose valves 64, 69, 71, 72 and 73. Valve 103 is then manipulated so asto permit a power source to place controllers 82, 83, 84, 85, 86 and 87in operation. Each control operates to initially open each of the valvesto which it is connected. The controllers are also operatively connectedto the pressure drop sens- -wardly through the shallow mass of pebblesin the upper portion of the bed within the elevator at such a volume andvelocity as to entrain the pebbles within the elevator. As the pebblesbecome entrained in the gas stream, the

pressure drop across pressure drop sensing element 81 decreases so as topermit a signal to be transmitted to controller 87. Controller 87 causesvalve 101 to be closed in response to the pressure drop across element81 thus making the path of least resistance for the gas through conduit93. This procedure is repeated until the pebbles 'are fluidized withinelevator 18.

Controls on valves 69, 71, 72, 73 and 64 may be main tained individuallyso that additional gas can be introduced into the portion of elevator 18containing the fluidized pebble portion so as to augment the singlestream flowing through the selected startup conduit. Once the pebblesare entrained within elevator 18, all of the auxiliary inlet conduitsare opened to gas flow by manipulation of valve 102 and the startupsystem is then closed by the manipulation of valve 103.

In the operation of the device shown as Figure 3 of the drawings, valve102 is manipulated so as to allow a source 'of power to close valves 64,69, 71 and 73. Valve 12 3 'is then manipulated so as to permit a powersource to *place differential controllers 115, 116, 117, 118, 119 and-121 in operation. 'open' one of the valves to which it is connected. As:pointed outabove, gas tends to take the path of least Each controlleroperates to initially resistance. Therefore,,with valve 72 remainingopen, the gas tends to take the path through conduit 67 above thethermocouples except for thermocouple 107. For this reason thermocouple107 indicates a higher temperature than thermocouple 108 and ittherefore imposes a temperature differential on differential controller115. Valve 122 is manipulated so as to cause valve 72 to be at leastpartially closed, thereby causing at least a portion of the hot gas toflow through conduit 94 and valve 101. As the gas flows through conduit94 into the elevator and fluidizes the pebbles within the section abovethat conduit, thermocouple 108 indicates a temperature substantially thesame as that indicated by thermocouple 107. As the temperaturedifferential between the measurements indicated by thermocouple 107 andthermocouple 108 diminishes to a predetermined minimum, differentialcontroller 11S operates to cause valve 101 to be closed. This causes thegas to pass through conduit 93 and valve 99 into the pebble mass inelevator 18, thus fluidizing the pebble mass above conduit 93. In thismanner, thermocouple 109 is raised to substantially the same temperatureas that indicated by thermocouple 108. As the temperature differentialbetween these two thermocouples diminishes to a predetermined minimum,differential controller 116 operates so as to close valve 99. Theremaining portion of the startup system operates in the same manner.

In another modification of this invention, valves 95, 96, 97, 98, 99 and101 can be selectively operated in accordance with a timing device so asto successively close the valves from the uppermost valve to thelowermost valve so as to obtain successive fluidization of smallportions of the pebble mass formed within the elevator.

Many additional modifications of this invention will be apparent uponstudy of the disclosure and the drawings. These modifications arebelieved to be within the spirit and the scope of this invention.

I claim:

1. An improved pyrolysis system which comprises a closed, upright,elongated shell; a pebble inlet in the upper end of said shell; gaseouseffluent means in the upper end of said shell; pebble outlet means inthe lower end of said shell; gaseous material inlet means in the lowerend portion of said shell; pebble feeder means intermediate the ends ofsaid pebble outlet means, an upright gas-pebble conduit connected at itslower end portion to the lower end of said pebble outlet means andextending to a level above the top of said shell; a gas-pebble separatorchamber connected to the upper end of said gas-pebble conduit;

a first pebble conduit extending between said pebble inlet 1 and thelower end portion of said separator chamber; a

lift-gas feed line connected to the lower end of said gaspebble conduit;a plurality of first lift-gas inlet conduits spaced along saidgas-pebble conduit; a plurality of second' lift-gas inlet conduitsspaced along at least the lower one-third of said gas-pebble conduiteach having a valve therein; means for operating said valvesindependently of each other and independently of flow in said firstinlet conduits; and gaseous material efi luent means extending from theupper end portion of said separator chamber.

2. The improved pyrolysis system of claim 1 wherein a heating gas inletconduit is connected to said first pebble conduit intermediate its ends;and a gaseous effluent conduit is connected to said first pebble conduitnear its upper end.

3. An improved pyrolysis system which comprises a closed, upright,elongated shell; pebble inlet means in the upper end of said shell;gaseous eflluent means in the upper end of said shell; pebble outletmeans in the lower end of said shell; gaseous material inlet means inthe lower end portion of said shell; pebble feeder means intermediatethe ends of said pebble outlet means; an upright gas-pebble conduitconnected at its lower end portion to the lower end of said pebbleoutlet means and extending to a level above the top of said shell; agaspebble separator chamber enclosing the upper end portion of saidgas-pebble conduit; a first pebble conduit extending between said pebbleinlet and the lower end portion of said separator chamber; a lift-gasfeed line connected to the lower end of said gas-pebble conduit; aplurality of first lift-gas inlet conduits spaced apart along the entirelength of said gas-pebble conduit; a plurality of second lift-gas inletconduits connected to said gaspebble conduit at spaced. intervals alongat least the lower one-third of said gas-pebble conduit and connected tosaid lift-gas feed line; a valve in each of said second lift-gas inletconduits; and, at least one controller operatively connected to each ofthe valves in said lift-gas inlet conduits, each of the controllersbeing responsive to sensing means sensitive to a variable physicalcondition of the gas in said gas pebble conduit at levels commensuratewith the levels of their respective lift-gas inlet conduits so as tosuccessively close said valves in the order of the uppermost to thelowermost of said valves when said variable condition progressivelychanges in the same order.

4. The improved pyrolysis system of claim 3 wherein a plurality oftemperature sensitive elements is spaced apart along at least the lowerone-third of the length of said gas-pebble conduit, said first lift-gasinlet conduits and said second lift-gas inlet conduits are connected tosaid gas-pebble conduit intermediate adjacent temperature sensitiveelements; and a temperature differential controller is operativelyconnected to adjacent temperature sensitive elements and to the valve inthe second liftgas inlet conduit immediately below the lowermost of eachpair of adjacent temperature sensitive elements.

5. The pyrolysis system of claim 4 wherein the uppermost of said firstlift-gas inlet conduits is connected to said gas-pebble conduitintermediate the two uppermost temperature sensitive elements; andincluding a valve in the uppermost lift-gas inlet conduit.

6. The pyrolysis system of claim 3 wherein a pressure drop sensing unitis operatively connected to said gaspebble conduit immediately aboveeach of said second lift-gas inlet conduits; and a controller isoperatively connected to each pressure drop sensing unit and operativelyconnected to the valve in said second lift-gas conduit immediately belowthe pressure drop sensing unit.

7. An improved pyrolysis system which comprises a closed, upright,elongated shell enclosing a single pebble heat-exchange chamber forheating gases by direct heat exchange; a pebble inlet in the upper endof said shell; gaseous eflluent means in the upper end of said shell;pebble outlet means in the lower end of said shell; gaseous materialinlet means in the lower end portion of said shell; pebble feeder meansintermediate the ends of said pebble outlet means; an upright gas-pebbleconduit connected at its lower end portion to the lower end of saidpebble outlet means and extending to a level above the top of saidshell; a gas-pebble separator chamber enclosing the upper end portion ofsaid gas-pebble conduit; a first pebble conduit extending between saidpebble inlet and the lower end portion of said separator chamber; alift-gas feed line connected to the lower end of said gaspebble conduit;a plurality of first lift-gas inlet conduits spaced along the length ofsaid gas-pebble conduit; a plurality of second lift-gas inlet conduitsconnected to said lift-gas feed line and to said gas-pebble conduit atspaced points along at least the lower one-third thereof; a valve ineach of said second lift-gas inlet conduits; at least one controlleroperatively connected to each of said valves in said second lift-gasinlet conduits, each of the controllers being responsive to sensingmeans sensitive to a variable physical condition of the gas in said gaspebble conduit at levels commensurate with the levels of theirrespective lift-gas inlet conduits; a second separator chamber; aneffluent conduit extending from the upper end portion of said separatorchamber to a point intermediate the ends of said second separatorchamber; a

:first indirect heat exchanger; a gaseous efiluent conduit extendingbetween the upper end portion of said second separator chamber and saidfirst indirect heat exchanger; efl luent outlet means extending fromsaid first indirect heat exchanger; a feed conduit extending throughsaid first indirect heat exchanger and connected to said gaseousmaterial inlet means in the lower end portion of said shell; a heatinggas inlet connected to said first pebble conduit intermediate saidpebble inlet means and said separator chamber; a gaseous efiluentconduit extending from the upper end portion of said first pebbleconduit; a furnace; combustible material inlet means connected to saidfurnace; and conduit means connecting said furnace and said heating gasinlet to said lift-gas inlet means.

8. The pyrolysis system of claim 7 wherein said gaseous effiuent conduitfrom said first pebble conduit is connected at its downstream end tosaid first indirect heat exchanger.

9. The pyrolysis system of claim 7 wherein a second indirect heatexchanger is operatively connected to said feed gas conduit intermediatesaid first indirect heat exchanger and said shell; a gaseous materialconduit extends between said furnace and said second indirect heatexchanger; and effluent conduit means extends from said second indirectheat exchanger.

10. An improved pyrolysis system which comprises a closed, upright,elongated shell enclosing a single pebble heat-exchange chamber forheating gases by direct heat exchange; a pebble inlet in the upper endof said shell; gaseous material efiluent means in the upper end of saidshell; pebble outlet means in the lower end of said shell; gaseousmaterial inlet means in the lower end portion of said shell; pebblefeeder means intermediate the ends of said pebble outlet means; anupright gaspebble conduit connected at its lower end portion to thelower end of said pebble outlet means and extending to a level above thetop of said shell; a gas-pebble separator chamber enclosing the upperend portion of said gas-pebble conduit; a first pebble conduit extendingbetween said pebble inlet and the lower end portion of said separatorchamber; a lift-gas feed line connected to the lower end of saidgaspebble conduit; a plurality of first lift-gas inlet conduits spacedalong the length of said gas-pebble conduit; a plurality of secondlift-gas inlet conduits connected to said lift-gas feed line and to saidgas-pebble conduit at a plurality of points spaced along at least thelower one-third of the length thereof; a valve in each of said secondliftgas inlet conduits; at least one controller operatively connected toeach said valve in said second lift-gas inlet conduits, each of thecontrollers being responsive to sensing means sensitive to a variablephysical condition of the gas in said gas pebble conduit at levelscommensurate with the levels of their respective lift-gas inletconduits; a second separator chamber; a conduit extending between theupper end portion of said gas-pebble separator chamber and a pointintermediate the ends of said second separator chamber; a first indirectheat exchanger; a conduit extending between the upper end portion ofsaid second separator chamber and said first indirect heat exchanger; agaseous effluent conduit extending from said first indirect heatexchanger; a feed gas conduit extending through said indirect heatexchanger and connected at its downstream end to said lift-gas inletmeans; a furnace; combustible material inlet means connected to saidfurnace; gaseous efiluent conduit means extending from said furnace; asecond indirect heat exchanger operatively connected to said furnace; afirst lift-gas conduit connected to the upstream end of said secondindirect heat exchanger; a second lift-gas conduit extending between thedownstream end of said second indirect heat exchanger and said lift-gasinlet means; and a pressurizer intermediate the ends of said firstlift-gas conduit.

11. The pyrolysis system of claim 10 wherein a third indirect heatexchanger is operatively connected to said feed conduit intermediatesaid first indirect heat exchanger and said shell; a conduit extendingbetween the downstream end of said furnace and said third indirect heatexchanger; and a gaseous efiiuent conduit extending from said thirdindirect heat exchanger.

12. The pyrolysis system of claim 10 wherein a heating gas inlet isconnected to said first pebble conduit intermediate said pebble inletmeans and said gas-pebble separator chamber; a gaseous material efiiuentconduit extending from the upper end portion of said pebble conduit,connected to said efiluent conduit from said first indirect heatexchanger; and a heating material conduit extending from said secondlift-gas conduit intermediate said second indirect heat exchanger andsaid lift-gas inlet means to said heating gas inlet in said first pebbleconduit.

13. The pyrolysis system of claim 12 wherein said gaseous materialconduit extends from the upper end portion of said first pebble conduitand is connected to said effiuent conduit from said first heat exchangerthrough said first heat exchanger.

14. The pyrolysis system of claim 12 wherein a gaseous material conduitextends between said effluent conduit from said first indirect heatexchanger to said first heating gas inlet conduit upstream of saidpressun'zer.

15. The pyrolysis system of claim 10 wherein said furnace is a tubefurnace; and said first lift-gas conduit and said second lift-gasconduit are connected to the tubes of said furnace at the upstream anddownstream ends, re-

.spectively.

16. An improved method for operating a pebble heater which comprises thesteps of introducing pebbles into the upper end of a single chamber;gravitating said pebbles downwardly through said chamber as acontiguous, gaspervious mass; gravitating said pebbles from the lowerend of said chamber at a controlled rate into the lower end portion of agas lift conduit; introducing a portion of a gaseous entraining fluidinto the lower end portion of said gas lift conduit, below the point ofingress of pebbles thereto, at a temperature of at least 2000 F. and insufficient volume to entrain said pebbles and to elevate said pebblesonly a portion of the distance to the upper end of said gas liftconduit, whereby the temperature of said pebbles is elevated by directheat exchange with said hot gaseous entraining fluid; introducingadditional portions of said 'hot gaseous entraining fluid into said gaslift conduit at spaced points along the length thereof, whereby thetemperature of said pebbles is continuously elevated to a desiredtemperature by direct heat exchange with said hot gases and with lessthermal and mechanical shock to said pebbles than would be effected byintroduction of all of said lift gas into said lower end portion of thegas-lift conduit; separating said lift-gas and said pebbles at the upperend of said gas lift conduit; gravitating said heated pebbles through acommunication zone into the upper end portion of said single chamber;introducing a gaseous feed into the lower end portion of said chamber;passing said gaseous feed upwardly through said contiguous, gas-perviouspebble mass within said chamber countercurrent to the gravitating pebbleflow, whereby said gaseous material is elevated to a desired temperaturewithin said chamber, and removing gaseous effluent from the upper endportion of said chamber.

17. The method of claim 16 wherein combustible materials are burned soas to produce hot combustion products and said combustion products areintroduced into the lower end and at points spaced along the length ofsaid gas lift conduit at a temperature within the range of 2000 F. to3200 F.

18. The method of claim 16 wherein said combustion products areintroduced into the lower end and at points v spaced along the lengthofsaid gas lift at a temperature of at least 2400 F.

, steamproduct is introduced into the lower end and at points spacedalong the length of said gas lift conduit.

20. The method of claim 19 wherein a portion of said combustion productsis introduced into the gravitating mass of pebbles intermediate the endsof said communication zone and is passed upwardly through suchgravitating mass of pebbles to a point near the upper end of said gaslift conduit; and the gaseous effluent is removed from the upper endportion of said communication zone adjacent the upper end of said gaslift conduit.

21. The method of claim 16 wherein said feed gas is preheated byindirect heat exchange with said gaseous effluent from said gas liftconduit.

22. The method of claim 16 wherein said lift gas is heated to atemperature within the range of between 2000 F. and 3200 F. in indirectheat exchange with combustible materials in a combustion chamber.

23. The method of fluidizing a static pebble mass within a gas liftconduit which comprises the steps of introducing hot gaseous materialinto the upper portion of said pebble mass within said gas lift conduitin suflicient volume to entrain said upper portion of pebbles in saidgaseous material; at least partially stopping the flow of gaseousmaterial directly into the fluidized portion of the pebble mass andintroducing additional hot lift-gas successively in the lower sectionsof said pebble mass with concomitant reduced flow of gas directly intothe fluidized portion, whereby said total pebble mass is heated andcompletely entrained.

24. The method of claim 23 in which said lift-gas is at a temperature inthe range of 2000 to 3200 F.

25. An improved pyrolysis system which comprises a closed, upright,elongated shell; a pebble inlet in the upper end of said shell; gaseouseflluent means in the upper end of said shell; pebble outlet means inthe lower end of said shell; gaseous material inlet means in the lowerend portion of said shell; pebble feeder means intermediate the ends ofsaid pebble outlet means; an upright gas-pebble conduit connected at itslower end portion to the lower end of said pebble outlet means andextending to a level above the top of said shell; a gas-pebble separatorchamber connected to the upper end of said gas-pebble conduit; a firstpebble conduit extending between said pebble inlet and the lower endportion of said separator chamber; a furnace outside of said gas-pebbleconduit and outside of said shell for producing hot lift gas; a lift-gasfeed line connecting said furnace with said gas-pebble conduit below thejuncture of said pebble outlet means with said gas-pebble conduit; aplurality of lift-gas inlet conduits connected with said gas-pebbleconduit at vertically spaced-apart points along its length and with ahot gas source; and a gas outlet means from an upper section of saidseparator chamber.

26. A method of fiuidizing a static column of pebbles within an uprightgas-lift conduit which comprises the steps of introducing a hot lift gasinto an upper portion of said column of pebbles within said gas-liftconduit in sufficient volume and flow rate to entrain said upper portionof said column of pebbles in said hot lift gas; thereafter introducingadditional hot lift gas successively in progressively lower sections ofsaid column of pebbles so as to entrain said column of pebbles in said'hot lift gas and elevate the same to the upper end of said conduit.

References Cited in the file of this patent UNITED STATES PATENTS1,123,155 Woodley Dec. 29, 1914 1,202,088 Murray Oct. 24, 1916 1,232,393Piper July 3, 1917 1,280,780 Lob Oct. 8, 1918 2,405,395 Bahlke et al.Aug. 6, 1946 2,432,503 Bergstrom et al Dec. 16, 1947 2,499,704 Utterbacket al. Mar. 7, 1950 2,509,983 Morrow May 30, 1950 2,548,030 Leifer Apr.10, 1951 2,548,522 Drew Apr. 10, 1951 2,585,984 Alexander et al Feb. 19,1952 2,587,670 Weinrich Mar. 4, 1952 2,614,028 Schaumann Oct. 14, 19522,626,141 Grossman Jan. 20, 1953 2,643,216 Findlay June 23, 19532,684,873 Berg July 27, 1954 2,703,732 Schut-te Mar. 8, 1955

25. AN IMPROVED PYROLYSIS SYSTEM WHICH COMPRISES A CLOSED, UPRIGHT,ELONGATED SHELL; A PEBBLE INLET IN THE UPPER END OF SAID SHELL; GASEOUSEFFLUENT MEANS IN THE UPPER END OF SAID SHELL; PEBBLE OUTLET MEANS INTHE LOWER END OF SAID SHELL; GASEOUS MATERIAL INLET MEANS IN THE LOWEREND PORTION OF SAID SHELL; PEBBLE FEEDER MEANS INTERMEDIATE THE ENDS OFSAID PEBBLE OUTLET MEANS; AN UPRIGHT GAS-PEBBLE CONDUIT CONNECTED AT ITSLOWER END PORTION TO THE LOWER END OF SAID PEBBLE OUTLET MEANS ANDEXTENDING TO A LEVEL ABOVE THE TOP OF SAID SHELL; A GAS-PEBBLE SEPARATORCHAMBER CONNECTED TO THE UPPER END OF SAID GAS-PEBBLE CONDUIT; A FIRSTPEBBLE CONDUIT EXTENDING BETWEEN SAID PEBBLE INLET AND THE LOWER ENDPORTION OF SAID SEPARATOR CHAMBER; A FURNACE OUTSIDE OF SAID GAS-PEBBLECONDUIT AND OUTSIDE OF SAID SHELL FOR PRODUCING HOT LIFT GAS; A LIFT-GASFEED LINE CONNECTING SAID FURNACE WITH SAID GAS-PEBBLE CONDUIT BELOW THEJUNCTURE OF SAID PEBBLE OUTLET MEANS WITH SAID GAS-PEBBLE CONDUIT; APLURALITY OF LIFT-GAS INLET CONDUITS CONNECTED WITH SAID GAS-PEBBLECONDUIT A VERTICALLY SPACED-APART POINTS ALONG ITS LENGTH AND WITH A HOTGAS SOURCE; AND A GAS OUTLET MEANS FROM AN UPPER SECTION OF SAIDSEPARATOR CHAMBER.